350 is your best bet here.
If you want a 454 you can find them with a rv cam in a rv for much cheaper then finding just the engine.
This also applies to a 8100 engine.
A bread truck for a 4bt mated to a sm465. Might sound like a great idea. But been there done that. Your mileage is not great, thing becomes really heavy, parts are expensive, and with a 4wd your running into clearence issues.